This invention relates generally to a flexible polymeric membrane. More particularly, this invention relates to a flexible polymeric membrane for a roof or in other applications such as fluid containment liners and covers (e.g., reservoir and land fill lines and covers).
While the present invention will be described in connection with a roof application, it will be appreciated that the roof membrane disclosed herein may also be useful in other applications requiring weldable, water resistant, chemical resistant polymeric membranes.
In certain modern roofing installations for commercial buildings, a layer of insulation is secured to the deck of the roof and then is covered with sheets of flexible material. Adjacent margins of adjacent sheets are sealed together (e.g., heat welded) in overlapping relationship and thus the sheets form a sealing membrane over the insulation.
The sheets which form the membrane are secured to the insulation and the underlying roof deck at spaced locations by fastener assemblies which are spaced along the margins of the sheets. Each fastener assembly comprises a washer-like disc and further comprises a screw adapted to thread into the roof deck to cause the disc to clamp the membrane downwardly against the insulation.
Typical roof membranes have been made from polyvinylchloride (PVC), vulcanized ethylene-propylene/diene (EPDM), chlorosulfonated polyethylene (Hypalon by DuPont), and chlorinated polyethylene (CPE). Less typically, membranes have been made from polyisobutylene (PIB), neoprene and modified bitumens.
U.S. Pat. Nos. 4,910,245, 4,978,703 and 4,978,716 (the entire contents of which are incorporated herein by reference) disclose a roof membrane generally comprised of a blend of an amorphous chlorinated polyethylene (CPE) resin, a crystalline thermoplastic polyolefin (e.g., extra low density polyethylene) resin, a plasticizing material, and a vulcanizing package comprising an inorganic base and 2,5-dimercapto-1,3,4-thiadiazole or a derivative thereof. During manufacture, the CPE is dispersed in the polyolefin and the CPE is vulcanized to form a vulcanizate dispersed in the polyolefin. This vulcanizate polyolefin blend is then dispersed into additional CPE (which is not vulcanized) forming a partially crosslinked thermoplastic polyethylene vulcanizate. This material is processable in an internal mixer (such as Banbury Mixer) and may be calendered on conventional calendering equipment (e.g., rubber mill) to form continuous sheets suitable for use as single ply roofing and in other applications such as reservoir liners and the like. This material is sometimes referred to as a thermoplastic vulcanizate or TPV.
While well suited for its intended purposes, the above-described TPV material has certain drawbacks and deficiencies. For example, processing the TPV requires crosslinking of expensive vulcanizing packages such as the 2,5-dimercapto-1,3,4-thiadiazole. In addition, the TPV processing comprises a three stage mixing process which leads to undesirably long manufacturing time periods as well as high cost. This mixing process also requires a relatively precise mixing schedule in order to insure high quality. Because of the three stages of mixing, the maintenance of such quality standards at each stage can be difficult. Still another problem is that the discrete particles of the CPE vulcanizate (blended into the non-vulcanized CPE/polyethylene matrix) may not be suitably fused to form a bond to the matrix leading to reduced physical and chemical properties such as reduced weatherability and chemical resistance.
Yet another disadvantage relates to the sealability (heat welding) of the TPV material which is reduced because of the presence of the vulcanized CPE phase.